Television system



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A. C. STOCKER TELEVISION SYSTEM Filed Oct. 23, 1934 MAMAN;

May 28, 1940.

Patented May 28, 1940 TELEVISON SYSTEM Arthur C. Stocker, Haddon Heights, N. J., assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware .reputation october as, 1934., serial No. 749,510

7 Claims.

My invention relates to improvements in television systems.

In one form of television receiving system, a cathode ray tube is utilized to develop an image of the transmitted view. This tube is provided with a uorescent screen and with means for developing a ray of electrons and directing the ray at the screen. For the purpose of causing the ray to scan the screen, it is deflected simultaneously in the horizontal and vertical directions, in synchronism with the respective corresponding scanning actions at the transmitter. The tube is provided with means for focusing the ray to a relatively small spot on the screen, and is also provided with one or more electrodes whose function it is to accelerate the electrons toward the screen so they strike the latter at a relatively high velocity. in this way, the screen is caused to liuoresce at the particular elemental area thereof at which the ray is directed at any instant, the brillianoy of the spot developed being a function of the intensity of the ray, which is controlled by the incoming picture signals.

ln the systems of the character referred to, and particularlf' those requiring relatively high anode current at high voltages to obtain sufficient light on the screen for projection purposes, the intensity of the cathode ray is suiiicient to burn a spot on the fluorescent screen if it is continuously directed at this spot for even a fraction of a second. That is, if, on starting the apparatus, the intensity of the ray becomes nearly normal before the deflecting circuits begin to function to deflect the ray, it will burn and permanently ruin the uorescent screen. Furthermore, if, in shutting down, the deflecting circuits cease to function before the ray is cut off or at least reduced substantially in intensity, the screen will be damaged. Also, if there is a failure in the power supply, or a failure at some point in the system to render the defiecting circuits ineffective so that the ray is directed continuously at one spot on the screen, the latter will be burnt at this spot.

For the purpose of protecting the uorescent screens against burning by the cathode ray under the conditions explained, it has been proposed to provide automatic means for cutting off the ray upon failure of the deecting circuits, or for maintaining the ray at cut-oli" until the deecting circuits are functioning properly, in starting up, or for cutting off the ray before the deflecting circuits cease to function, in shutting down. These automatic systems proposed heretofore, however, require the use of complicated switching actions, the use of relays, and, generally, are

(Cl. Z50-27) unreliable for faithful service over a long period of time.

With the foregoing in mind, it is one of the objects of my invention to provide an improved television system of the character referred to wherein provision is made for protecting the fluorescent screen against burning by automatic means effective to cut olf the ray upon loss of defiection, to maintain the ray at cut off until the deflecting circuits begin to function properly in starting up, or to cut off the ray as the reiiecting circuits cease to function in shutting down.

Another object of my invention is to provide an improved television system of the character referred to wherein provision is made for cutting off the ray, for the purpose explained, by means which are automatic and also relatively simple in construction and in operating action, and which are reliable in operation.

Other objects and advantages will hereinafter appear.

In accordance with my invention, the bias on the electron gun for cutting off the ray is supplied by a filter circuit having a predetermined time constant of operation. tials supplied to the anodes of the tube, for accelerating the ray toward the screen, are supplied from a second filter having a time constant of operation substantially greater, that is, longer, than that of the first filter. The arrangement and operating action are such that upon closing the switch to the common power supply, in starting up, the bias on the grid of the electron gun builds up at a substantially higher rate than the first and second anode voltages. In this way, the anode current is reduced to a safe value, at which the screen is not damaged although the defiecting circuits might not be operating. When the deiiecting circuits begin to function properly, the bias is reduced automatically so that the ray is then at normal intensity. Upon failure of the defiecting circuits for any reason, the bias is increased automatically to cut off the ray. When the main power switch is opened, such as in shutting down, the bias builds up automatically to cut off the ray, and then decays at a rate substantially lower than the rate of decay of the respective voltages on the first and second anodes, whereby the anode current is kept at a safe value as the deecting circuits cease to function.

My invention resides in the improved system and method of operation of the character hereinafter described and claimed.

For the purpose of illustrating my invention, an

The positive poten- 2 embodimentJ thereof is shown in the drawing, wherein:

Figure 1 is a simplified, diagrammatic View of a television receiving system constructed and operating in accordance with my invention and Fig. 2 is a graphical View, illustrative of the principle of operation of the system shown in a fluorescent screen l2 and an electron gun Hl for developing a cathode ray Iii and directing the same at the screen. The gun is provided with a control grid iii to which incoming picture signals and horizontal and Vertical synchronizing signals are applied by way of a connection 20 from a receiver 22.

A biasing potential is' applied to the grid i8 through a grid leak 2d connected to a resistor 26 by an adjustable contact 28.

For the purpose of causing the ray It to scan the screen l 2, a saw-tooth current Wave at a relatively high frequency, generated by a circuit designated at tais caused to pass through electromagnetic coils 32. Simultaneously Ywith this action, a saw-tooth Wave at a relatively low fre- A quency, generated by a circuit designated at 30, is caused to pass through electromagnetic coils 35.

The receiver 22 operates to separate the horizontal synchronizing signals from the other in-I coming signals, and to supply only these by way of a connection iQ to the circuit 34. These signalsare effective to drive the circuit 34 and maintain operating action of the same in' synchronism with operating action of the corresponding circuit at the transmitting station.

Likewise, the receiver 22 operates to separate the vertical synchronizing signals from the other signals, and to supply only these by way of a connection 38 to the circuit 3K2. This circuit is driven by the vertical synchronizing signals, and operating action thereof is maintained thereby in synchronism with operating action of the corre-` sponding circuit at the transmitter.

The incoming horizontal and vertical synchronizing signals are of the same polarity as, but are greater in amplitude than the incoming picture signals representative of conditions of shade at the transmitter. Under such conditions, these signals are applied to the grid Yi8 of the electron gun.

As the ray it is causedto scan the screen I 2 along horizontal lines from left to right, looking toward the right `in Fig. 1, and downwardly, a horizontal synchronizing signal occurs at the end of each horizontal line, and as the ray begins its return deflection to the left. A vertical synchronizing signal occurs at the end of each frame when the ray is directed at the lower right-hand corner of the screen, looking toward the right in Fig. 1, and as the ray begins its return deiiection back to the starting point at the upper left-hand corner of the screen. In this way, a negative potential is applied to the ygrid I8 suii'cient to substantially'cut ofi' the ray during return deection thereof in both the horizontal and Vertical directions.

The details of circuits suitable for deilection of the ray, and a detailed explanation of the nature tion, noadditional explanation of the same is believed to be necessary.

The tube l!) is provided with a rst anode 42 which forms part of the electron gun iii, and with a second anode 44 in the form of a metallic coating on the inside surface of the tube. In operation, a. potential positive with respect to the cathode i6 of the electron gun is applied to the anode i2 by a connection 48 from a tap on a resistor 59. A potential, considerably more positive than the potential on the first anode d2, is applied to the second anode M by a connection 52 from the resistor 50. Under these conditions, the ray I6 is focused to a relatively small spot on the screen i2. The rst anode ft2 is effective to accelerate the electrons toward the screen. The anode lill, at the higher positive potential, is eiiective to further accelerate the electrons toward the screen.

Operating power for the system is obtained from a common alternating current supply connected through a switch 56 to the primary 53 oi a transformer 69. A filter 6ft is connected across a portion of the secondary winding 62 through a rectifier tube 655, and feeds a load comprising the resistor 2t and a second resistor 68 connected to ground, as represented.

The high voltage winding 62, a rectifier tube l and a lter l2 comprise the supply potential for the receiver 22 through a connection lf3, and the ,y Vpotential supply for the circuits 3i! and 34 The resistor 50 is supplied from a lter all, rectii'ier tubes 86 and a secondary winding 88 of the power transformer.

The condensers and 82 of the lter 64 and the resistors 26 and 68 are so proportioned with respect to the condensers and 92 of the filter 8@ that on removal of the supply power, the bias voltage at the contact 28 decays more slowly than the voltage at the point 94 which is applied to the rst anode 42 and the voltage at the point 9S which is applied to the second anode 1M. In other words, the iilter 64 and associated parts, for supplying the bias to the electron gun lll has a ltime constant of operation, in shutting down,y

substantially greater than the time constant of operation of the lter 84 and lassociated parts for supplying the operating potentials to the first anode 42 and the second anode 64.

' Also, the condensers 8l] and 82, the resistor of the lter 64, and the internal resistance of the rectifier tube 66, are so proportioned with respect to the condensers Sii and 92, the resistor of the filter 84,'and the internal resistance of the associated rectier tubes 86, that upon application of the supply power, in starting up, the bias voltage at the contact 28 builds up more rapidly than the voltages at the points 94 and 9S. The filter Sli and associated parts for supplying the bias to the electr-0n gun id, therefore, have a time constant of operation, in starting up, substantially smaller, that is, shorter, than the time constant of `operation of the filter 84 and associated parts for supplying the operating potentials to the first anode ft2 and the second anode 44. The reason for this will hereinafter more fully appear.

The plate' of ar bias detectortube 98 is supplied, through a filter |00 and a connection E62, from themain plate supply from the filter 12. This tube is biased to cut-off through a grid resistor H14 connected .by a-contact Ito the resistor 26.

The grid of the tube 98 is coupled to the hori- Zontal deflecting coils 32 through a condenser |08.

The plate of a second bias detector tube H is supplied, through a filter ||2 and the connection |02, from the main plate supply from the lter 72. The tube Hd is biased to cut-ofi through a grid resistor Hd connected as shown to the contact IBS. The grid of the tube H0 is coupled through a condenser HS to the vertical deecting coils 3S.

The various adjustments and the construction of the tubes d5 and 8E are such thatthe filament of the tube E6 becomes hot at least as soon as the filaments of the tubes BS. When the switch 56 is closed, therefore, the tube 66 begins to dra-W current and to operate at least as soon as the tubes 86.

The bias supplied to the grid i8 from the resistor 2t, and which is required for cutting-oli" the ray H5, is always a deiinite percentage oi the voltage on the rst anode 42.

All tubes in both deflecting circuits 3i) and 3d and in the receiver 22 have their cathodes connccted to ground.

The operation of the system will now be eX- plained, with reference to Fig. 2, in which the percentage .of biasing potential on the grid iii and the percentage of potential on the second anode lid are plotted against time. One hundred percent bias on the grid i8 is suflicient to cut off the ray with one hundred percent or" the normal operating voltage on the second anode M.

When the switch 56 is closed in starting, the bias on the grid |8 builds up in a manner represented by the curve iB in Fig. 2, and at a greater rate than the voltage on the second anode M, which builds up in a manner represented by the curve |293. During this time, therefore, the-tube 98 is cut oii. When the horizontal deflecting circuit Zit begins to function effectively at the point mi in Fig. 2, the alternating current voltage across the deiiecting coils 32 is impressed on the grid ci the tube 9S to cause it to pass plate current, thereby causing the voltage at the point |22 to become substantially less negative with respect to ground. The voltage at the contact 2t therefore becomes substantially less negative with respect to ground whereby the bias on the grid i3 is reduced to the point, represented at #23, whereat the intensity of the ray is normal. From this it will be seen that in starting up the screen i2 is protected, since the bias on the grid i8 builds up at a substantially greater rate than the potential on the second anode 44.

If there is a failure due, for example, to the burning out of a tube in the deflecting circuit 30, or to the occurrence in this circuit of a shortcircuit to ground, or the loss of B supply to this circuit, the tube 98 is automatically cut off to cause the voltage at the point |22 to become more negative and, accordingly, the biasing potential at the contact 28 to become substantiallyr more negative to cut off the ray. The bias on the grid |8 then increases, as represented by the curve i2t, to the value of one hundred percent bias, whereat the ray is out oii and the screen l2 protected at this time, when the deiiecting circuit tli is ineffective.

When the switch 56 is opened, in shutting down, the defiecting circuit 3E! ceases to operate, and the bias on the grid I8 increases to the cutoi value, as just explained, from the point |23 and along the curve |26 to the point |28. The bias on the grid i8 then decreases as represented by the curve i3d, at a substantially lower rate than the decay of the voltage on the second anode Btl, as represented by the curve |32. In shutting down, there is therefore always suiiicient bias on the grid |8 to keep the intensity of the ray I6 sufciently low so that the screen |2 is protected against burning as the voltage on the second anode 44 decays.

The operating action with respect to the tube l iii is the same as that just explained in connection with the tube 98. That is, the tube llil, which is responsive to conditions of voltage across the vertical delecting coils 36, is effective to cause the ray i@ to be cut off upon failure of the circuit Bd to supply the required operating voltage to the coils 36.

From the foregoing it will be seen that I have provided an improved television receiving sysembodying a cathode ray tube, in which means are provided for protecting the uorescent screen against burning by the ray by cutting off the ray in starting until the deecting circuits began to operate, by cutting oi the ray in shut ting down, until the operating potentials on the anodes of the cathode ray tube decay to safe values, and by cutting-off the ray in the event of failure of deiiection during operation.

While I have disclosed my invention in connection with a television receiving system, it will be understood that the same has a much broader aspect, and might be embodied to advantage in a transmitting system having a cathode ray tube for developing the picture signals, or in connection with a cathode ray oscillograph to protect the screen thereof.

Furthermore, it will be understood that various modifications, within the conception of those skilled in the art, are possible without departing from the spirit of my invention and the scope of the claims.

I claim as my invention:

l. In combination, a tube provided with a screen and with means including an anode and a control electrode for developing a ray of electrons and directing the ray at said screen, means for deiiecting said ray, means for supplying a biasing potential to said control electrode to substantially cut oir said ray, means for supplying an operating potential to said anode to accelerate the electrons toward said screen, and means common with respect to said third-named and iourth-named means for supplying the same with operating power, said third-named means being characterized by the fact that upon removal of the operating power it has a time constant of operation substantially greater than the time constant of operation of said fourth-named means.

2. In combination, a tube provided with a screen and with means including an anode and a control electrode for developing a ray of electrons and directing the ray at said screen, means for deflecting said ray, means including a first filter circuit for supplying a biasing potential to said control electrode to substantially cut off said ray, means including a second lter circuit for supplying an operating potential to said anode to accelerate the electrons toward said screen, and means common with respect to said filter circuits for supplying the same with operating power, said third-named means and the first filter associated therewith having a time constant of operation substantially greater than the time constant of operation of said fourth-named means and the second filter associated therewith upon removal of the operating power.

3. In combination, a tube provided with a screen and with means for developing a ray of electrons and directing the ray at said screen, said means including a control electrode, said tube being provided with an anode for accelerating the electrons toward said screen, means for deiiecting said ray, means including a combination rectiiier-and-lter circuit for supplying an operating potential to said anode, means including a second combination rectier-and-filter circuit for supplying a biasing potential to said control electrode to substantially cut 01T said ray, and means common with respect to said circuits for supplying the same with operating power, said fourth-named means upon application of the operating power having a time constant of operation substantially smaller than the time constant of operation of said third-named means.

4. yIn combination, a tube provided with a screen and with means for developing a ray of electrons and directing the ray at said screen, said means including a control electrode, means for deflecting said ray, a circuit for supplying said deecting means with a voltage wave, means for supplying said control electrode with abiasing potential, a detector tube connected to said third-named means and biased substantially to cut oi thereby, and connecting means between said circuit and the grid circuit of said detector tube whereby the latter is caused to draw current only under conditions whereat said circuit is efiective for deecting said ray.

5. In combination, a tube provided with a screen and with means for developing a ray of electrons and directing the ray at said screen, means for deiiecting said ray, means for accelerating the electrons toward said screen and having a given time constant of operation, means for cutting ofi said ray and having a time constant of operation upon the application of power thereto substantially less than that of said accelerating means, and means controlled by said ray-deflecting means and operable responsive to effective ray-deiecting action of the latter to remove the iniuence of said fourth-named means whereby the intensity of said ray is caused to reach a value corresponding substantially to that for normal operation of said tube.

l 6. In combination, a tube provided with a screen and with means for developing a ray of electrons and directing the ray at said screen, said means including a control electrode, means for deiiecting said ray, means for supplying a biasing potential to said control electrode to substantially cut on said ray, means for supplying an operating potential to said tube to accelerate the electrons toward said screen, and means common With respect to said third-named and fourth-named means for supplying the same with operating power, said third-named means being characterized by the fact that upon removal of the operating power it has a time constant of operation substantially greater than the time constant of operation of said fourth-named means while upon application of the operating power said third-named means has a time constant of operation substantially less than the time constant of operation of said fourth-named means.

7. In combination, a tube provided with a screen and with means for developing a ray of electrons and directing the ray at said screen, said means including a control electrode, means for deflecting said ray, means including a first lter circuit for supplying a biasing potential to said control electrode to substantially cut off said ray, means including a second iilter circuit for supplying an operating potential to said tube to accelerate the electrons toward said screen, and means common with respect to said lter circuits for supplying the same with operating power, said third-named means and the rst filter associated therewith having a time constant of operation substantially greater than the time constant of operation of said fourth-named means and the second lter associated therewith Y,

upon removal of the operating power and having a time constant of operation substantially less than the time constant of operation of said fourth-named means and the second iilter associated therewith upon application of the operating power. i

ARTHUR C.` STOCKER. 

